1. Field of the Invention
The present invention relates to a dial switch disposed on a control panel, the dial switch being illuminated by a colored ring surrounding the dial switch.
2. Description of Related Art
An example of a switch disposed on a control panel for use in an automobile is disclosed in JP-A-2000-276967. An area around the switch is illuminated to improve visibility.
A dial switch which is illuminated by a multi-color ring has also been proposed. An essence of such a conventional dial switch is illustrated in FIG. 4 attached hereto. The dial switch includes a transparent ornamental prism J2 disposed at a front opening of a case J1 covering a control panel, light sources J9 supported on a printed circuit board J4, and a transparent light-conducting prism J3 disposed between the light sources J9 and the ornamental prism J2. The ornamental prism J2 is formed in a cylindrical shape having a flange J2c. The cylindrical portion of the ornamental prism J2 is inserted into a front opening of the case J1, and the flange J2c is connected to a rear surface of the case J1. A red layer J2a forming a half circle and a blue layer J2b forming another half circle are printed on the rear surface of the cylindrical portion.
The light-conducting prism J3 has a cylindrical portion and an inside plate portion having a center hole. The light-conducting prism J3 is disposed so that an axial end of its cylindrical portion faces the red layer J2a and the blue layer J2b. A rotary switch J7 having a shaft J6 and a dial knob J5 connected to the shaft J6 is mounted on the printed circuit board J4. The shaft J6 extends to a front side of the case J1 through the center hole of the light-conducting prism J3. The surface of the light-conducting prism J3 facing the front side is covered with a light-blocking layer J8 consisting of a white layer J8a as an under-layer and a black layer J8b as an over-layer.
In the daytime when the control panel is not illuminated, the red layer J2a and the blue layer J2b are visible from the front side of the case J1 because the ornamental prism J2 is transparent. Therefore, a front end of the ornamental prism J2 surrounding the dial knob J5 is colored in red for a half circle and in blue for another half circle. This enhances an ornamental design of the control panel. In the nighttime when the light sources J9 are lit, the light is led from the light sources J9 to the front circle surrounding the dial knob J5 through the light-conducting prism J3, the colored layers J2a, J2b and the ornamental prism J2. Therefore, the circle surrounding the dial knob J5 is illuminated by a colored ring. Thus, the ornamental design of the control panel is enhanced.
In the conventional dial switch illuminated by the colored ring, however, the front surface of the light-conducting prism J3 has to be covered with the light-blocking layer J8 consisting of the white layer J8a and the black layer J8b. The light-blocking layer J8 is formed by painting, for example. In the painting process, surfaces of the light-conducting prism J3, which are not covered with the light-blocking layer, must be masked. The painting process as a whole makes the manufacturing process complex. Further, in the conventional dial switch, the light from the light sources J9 leaks through the center hole of the light-conducting prism J3, a gap between the light-conducting prism J3 and the ornamental prism J2 and the flange J2c of the ornamental prism J2, as shown with arrows in FIG. 4. The light color leaked through these portions has a color of the light sources J9, and is different from the light color passing through the red layer J2a and the blue layer J2b. Therefore, ornamental effects of the colored ring are adversely affected by the leaked light.